TITLE:   GCN CIRCULAR
NUMBER:  35323
SUBJECT: GRB 231210B: MeerLICHT afterglow observations
DATE:    23/12/11 21:11:37 GMT
FROM:    Simon de Wet at University of Cape Town <simdewet@gmail.com>

S. de Wet (UCT), P.M. Vreeswijk (Radboud) and P.J. Groot (Radboud/UCT/SAAO) report on behalf of the MeerLICHT consortium:

The 0.6 m wide-field MeerLICHT optical telescope located in Sutherland, South Africa, obtained a repeated series of 60 s exposures in the q,u,g,r,i,z bands of GRB 231210B following the Swift detection (Page et al., GCN 35314). Observations started at 21:32:26 UT on 2023 November 18 (202 seconds post-trigger) and continued for a further 1.79 hours, following the filter sequence quqgqrqiqz. 

We detect the optical afterglow also detected by MASTER, UVOT, LCOGT, and the VLT (Buckley et al., GCN 35313; Page et al., GCN 35314; Pérez-Fournon et al., GCN 35316; Saccardi et al., GCN 35317) with the following AB magnitudes:

q = 17.15 +/- 0.02 at 21:32:57 UT
u = 19.67 +/- 0.19 at 21:34:20 UT
g = 18.69 +/- 0.04 at 21:37:17 UT
r = 18.11 +/- 0.03 at 21:40:11 UT
i = 18.15 +/- 0.05 at 21:43:08 UT
z = 18.30 +/- 0.11 at 21:46:05 UT

As a precaution, we note that the absolute photometric calibration may have been adversely affected by condensation in the cryostat window due to high humidity. Our high cadence q-band observations show a power-law decline with a temporal index of -1.2 throughout the observations. 

MeerLICHT is built and run by a consortium consisting of Radboud University, University of Cape Town, the South African Astronomical Observatory, the University of Oxford, the University of Manchester and the University of Amsterdam.